The present invention relates to a nanocomposite, and more particularly, to a nanocomposite composing of titanium aluminum carbon nitride and amorphous carbon.
In a micro view, material deformation is caused by dislocation glide, but it is not easy for ceramic material to have dislocation glide. When force is exerted on the ceramic material, the ceramic material is not easy to have dislocation glide, thus resulting in the phenomenon of stress concentration, so that cracks are very likely to be formed, wherein the brittle destruction appears. In order to overcome the shortcoming regarding the brittleness of ceramic material, nano-technologies developed recently have become one of the best choices.
Some studies indicate that: when the dimension of single material grain is decreased to the degree of nanometer, the material deformation can approach the degree of super-plasticity by room temperature creep. If the composite material is made by combining two or more phases of material, appropriate material types and the ratio thereof have to be selected, so as to increase the degree of plastic deformation via the gliding between the grains. The studies further indicate that: the adhesiveness of a nanocomposite composed of titanium carbide and amorphous carbon is superior to that of one single titanium carbide coating and that of one single amorphous carbon coating.
The nitrides and carbides of transition metals can be mutually dissolved to form carbon nitrides, and the properties of the carbon nitrides are varied in accordance with the value of [C]/[C]+[N]. Titanium carbon nitride (TiCN) has better wear resistance and toughness than titanium nitride, and titanium aluminum nitride (TiAlN) has better anti-oxidation and thermal hardness than titanium nitride. Both titanium carbon nitride and titanium aluminum nitride have the same rock salt structure as titanium nitride, wherein titanium carbon nitride is formed by substituting part of nitrogen atoms with carbon atoms, and titanium aluminum nitride is formed by substituting part of titanium atoms with aluminum atoms. The hardness and shear modulus of the rock salt structure material are related to the number of the valence electrons (i.e. valence electron concentration value; VEC value) of a cell unit in bonding. The VEC value of titanium nitride is 9, and the VEC value of titanium carbide is 8, and the VEC value of aluminum nitride with rock salt structure is 8. According to the experiment results and theoretical calculation, the previous studies indicate that: for a material having a VEC value between 8 and 9, the hardness and shear modulus thereof are increased; it can be thus inferred that the hardness and shear modulus of titanium aluminum carbon nitride (TiAlCN) are larger than that of titanium carbide; that of titanium nitride; and that of aluminum nitride, wherein the VHC value of titanium aluminum carbon nitride can be adjusted by changing the proportion of elements in titanium aluminum carbon nitride.
A nanocomposite can be a material of super hardness or of super toughness. For example, titanium nitride nanometer grains are separated via amorphous silicon nitride grain boundary of several nanometers in width. Since the size of nanometer grain is small, dislocations hardly exist in the internal thereof, and the gliding between the grains is further confined by the interaction force between the grains and the grain boundaries, the studies indicate that the hardness of titanium nitride nanocomposite can be equivalent to that of diamond.
Besides, in the actual application of hard coating, hardness is not the sole consideration. Generally speaking, the higher the hardness is, the lower the toughness is (such as diamond). If the material of super hardness falls off while in use, the substrate will suffer more sever damage. Although the material using amorphous carbon as matrix has worse overall hardness than the material of super hardness, yet with the properties of low friction coefficient of amorphous carbon and superior compatibility between amorphous carbon and grains, some studies have indicated that a composite composed of titanium carbide nanometer grains and an amorphous carbon matrix can increase the ductility and improve the adhesiveness of a coating. Therefore, it is expected that the ductility can be increased greatly by adding amorphous carbon into the coating of titanium aluminum carbon nitride as a matrix of nanometer grams.
On the basis of the aforementioned thought, the coating strength of a composite of titanium aluminum carbon nitride-amorphous carbon can be provided by titanium aluminum carbon nitride nanometer grains, and the great deformation of titanium aluminum carbon nitride-amorphous carbon can be provided by the gliding between the grains. Therefore, a superior toughness ceramic coating having superior strength and ductility can be developed, so that the ceramic coating can be used in making steel tools used under the cutting environment of high temperature and high speed, thereby enhancing the performance of tools and elongating the operation life thereof.
In view of the conventional materials having the drawbacks of easily occurring brittle destruction, the present invention provides a superior toughness and adhesive strength ceramic coating of titanium aluminum carbon nitride-amorphous carbon nanocomposite to overcome the drawback that the conventional ceramic material is brittle.
One major object of the present invention is to provide a nanocomposite composing titanium aluminum carbon nitride and amorphous carbon, and the nanocomposite comprises titanium aluminum carbon nitride grains with nanometer scale and an amorphous carbon matrix.
According to the above-mentioned conception, the structure of the titanium aluminum carbon nitride grains is double face-centered cubic packing structure.
According to the above-mentioned conception, part of the carbon elements exist in the titanium aluminum carbon nitride grains, and another part of the carbon elements constitute the amorphous matrix.
Another object of the present invention is to provide a method to coat a nanocomposite coating composing titanium aluminum carbon nitride and amorphous carbon on a substrate, the method comprising: depositing the substrate in a reaction chamber; injecting hydrogen carrier gas into the reaction chamber, and setting a plasma power and igniting plasma to clean and remove an oxide layer and adsorptive on the substrate; setting a temperature and injecting a reaction gas comprising nitrogen, methane, argon, titanium tetrachloride, and aluminum tichloride; and keeping an appropriate working pressure. The reaction gas is activated and thermal decomposed by plasma to form a nanocomposite coating of titanium aluminum carbon nitride-amorphous carbon on the surface of the substrate.
According to the aforementioned conception, the material of the substrate is selected from a group consisting of steel, silicon chip, glass, titanium alloy, and plastic.
According to the aforementioned conception, the hydrogen carrier gas can be replaced by nitrogen or argon.
According to the aforementioned conception, the plasma power is 100 watts.
According to the aforementioned conception, the temperature is set between 450xc2x0 C. and 550xc2x0 C.
According to the aforementioned conception, the working pressure is between 0.1 torr and 10 torrs.
According to the aforementioned conception, the thickness of nanocomposite coating of titanium aluminum carbon nitride-amorphous carbon is between 1 xcexcm and 5 xcexcm.
According to the aforementioned conception, the titanium aluminum carbon nitride is synthesized by titanium tetrachloride, aluminum trichloride, methane (or acetylene), and nitrogen (or ammonia).
According to the aforementioned conception, the amorphous carbon is synthesized by methane (or acetylene).
According to the aforementioned conception, the method for activating the reaction gas can use radio frequency plasma, direct current plasma, microwave, sputtering, or electric arc.
According to the aforementioned conception, the technique of the coating step can be replaced by a physical vapor deposition method, wherein a titanium target, an aluminum target, nitrogen, and methane are used as composition sources.